feat(api-extractor): support multiple entrypoints

[Qjuh]

Please describe the changes this PR makes and why it should be merged:

For eventual support of generating docs for discord-api-types or @discordjs/next this adds support for documenting API items from multiple entrypoints.

Status and versioning classification:

• This PR only includes non-code changes, like changes to documentation, README, etc.

[vercel]

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Name	Status	Preview	Comments	Updated (UTC)
discord-js	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	May 12, 2025 9:39pm

1 Skipped Deployment

Name	Status	Preview	Comments	Updated (UTC)
discord-js-guide	⬜️ Ignored (Inspect)	Visit Preview		May 12, 2025 9:39pm

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 42.61%. Comparing base (f6da949) to head (6e4c5a8).
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10829      +/-   ##
==========================================
+ Coverage   42.60%   42.61%   +0.01%     
==========================================
  Files         262      262              
  Lines       16129    16122       -7     
  Branches     1549     1549              
==========================================
- Hits         6871     6870       -1     
+ Misses       9246     9240       -6     
  Partials       12       12              

Flag	Coverage Δ
brokers	31.41% <ø> (ø)
builders	80.49% <ø> (ø)
collection	100.00% <ø> (ø)
core	0.89% <ø> (ø)
formatters	99.63% <ø> (ø)
proxy	65.88% <ø> (ø)
rest	87.76% <ø> (ø)
util	43.28% <ø> (ø)
utilities	100.00% <ø> (ø)
voice	70.90% <ø> (ø)
ws	36.29% <100.00%> (ø)

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